1. Field of the Invention
This invention relates generally to an Airborne Pulse Doppler Radar Missile Warning System and, in particular, to a distributed missile warning system having typically two to six antennas operating simultaneously and continuously with parallel transmit/receive modules, and parallel processing of the radar data to provide rapid detection and timely activation of counter-measures.
2. Description of Related Art
Conventional Airborne Pulse Doppler Radar Missile Warning Systems (MWS) use multiple, electrically small antennas to cover the required search volume. The antennas are electronically sequenced with a programmed dwell time. Centralized and common transmitter, receiver and signal processor elements are used to keep the costs affordable. The economic efficiency of this architecture made sense twenty-five years ago when these systems were developed and when the cost of these major components represented the major cost of the system. Limitations of this conventional architecture include lost duty factor and increased scan time for a specific antenna resulting from the need to sequentially service all antennas, compromises in the selection of pre and post detection integration times, and the necessity to run heavy, stiff and expensive low loss RF Cable to each antenna, a problem exacerbated on large aircraft. In addition, these systems did not contain high speed data processors to insure that a low false alarm rate could be maintained in operational environments.
U.S. Pat. No. 4,700,191, issued Oct. 13, 1987 to Dan Manor of Rehovot, Israel, discloses a radar warning receiver for detecting and analyzing radar signals comprising a plurality of channels, one for each RF head which receives an antenna signal from one of four antennas. Acquisition mode was performed on all four antennas simultaneously, but critical bearing analysis required a reconfiguration of the parallel channels of the receiver resulting in a faster system, but not fully parallel and not instantaneous in its coverage. Also, the parallel channels contain a significant amount of redundant, and low reliability, analog circuitry.
U.S. Patent Application Publication No. US2005/0030222, published Feb. 10, 2005, by inventor Fritz Steudel, discloses a method for determining the spin and precession rates for a spaceborne radar target following an exoatmospheric parabolic flight path. The range rate component due the parabolic flight path is calculated then subtracted from the actual target range rate estimate provided by the wideband band tracking radar. The residue signal is FFT'd and shows sinusoidal variations in range rate due to shifts in the target's range geoid. These shifts are caused by the composite spin and precession motions of the target. The present invention, in contrast, uses amplitude variations in the target signal strength to measure both the target missiles' seeker spin rate and the missile body roll stabilization rate. The total return from the missile is composed of three major backscattering components. First, a traveling-wave return travels to the end of the missile where it is reflected by the missile skin/air mismatched interface. It then travels back to the nose of the missile where it is re-radiated. The amplitude of this component is modulated by the number of wings that interrupt the surface wave path as the missile body rotates producing the second component. A third component is caused by the partially silvered mirror at the input to the missiles front-end seeker. This light modulator also modulates the amplitude of the missile's radar return as it spins. These latter two amplitude variations are measured by storing each potential target amplitude return for a quarter of a second, then FFT'ing the resulting waveform. When a target is declared after 0.25 seconds of tracking, the spin and roll rates for it are determined simultaneously using the FFT of the targets amplitude variations. This FFT also provides the phase of the spin, thus the actual look angle of the seeker's silvered input modulator. Knowledge of the phase angle greatly enhances the simplicity and effectiveness of a jamming IR light source. The difference between the prior art for a spaceborne target and the present Missile Warning System are major as described above.
U.S. Pat. No. 5,287,110, issued Feb. 15, 1994 to My Tran, and assigned to Honeywell, Inc., of Minneapolis, Minn., describes aircraft survivability equipment (ASE) software which correlates data received by various ASE subsystems including a pulsed radar jammer, continuous wave (CW) radar jammer and a missile approach detector to provide a comprehensive and coherent picture of the threat environment. The ASE controls a decoy dispenser. The refined direction of arrival (DOA) for a threat is taken from these three receivers. Aiding in the correlation process is the time of arrival (TOA) and/or the carrier frequency of the threat missiles ground based radar pulses, all of which are estimated by each of the RF receivers. Thus, ASE suite of passive sub systems utilizes redundant data from multiple sources to refine the average measurement for the overall suite of sub-systems. The disadvantage of this approach is that there is redundant hardware in the suite of equipments which are making the same measurements of the threat environment. Clearly Mr. Tran's approach is not an optimum design configuration either in terms of acquisition, reliability, maintainability, logistical programming or training. Its primary purpose is to correlate the data from multiple sensors for the user. The DOA measurement refinement is a secondary consideration.
However, in the present invention's active system, identical and inexpensive digital and data processors are operated simultaneously and in parallel to improve the detection range of threats while minimizing the time necessary to react to a target. The overall system's reliability is also improved by using the distributed low power transmitters and the highly reliable and redundant modern digital components for data acquisition and processing.
In addition, in this approach an optional feature to synergistically integrate with a multiple quadrant optical system has been provided. Accurate missile track data from the optical system, azimuth and elevation angles not available from the radar can be combined with the range, velocity and acceleration data from the radar, thus producing a full three-dimensional (3-D) track file. The major advantage of the “3D” file is more accurate verification of the threat missile flight path, thus enabling achievement of an ultra low false alarm rate.